Heretofore, a carburized hardening or an induction hardening is employed for a surface hardening treatment of steel. Both of these methods were of obtaining a hard martensitic structural component by heating steel up to the austenitic stage and followed by quick cooling of that steel, i.e. quenching ( see "Heat Treatment of Steel"]5th edition, pp. 253-266, 1985; Maruzen). As an apparatus therefor, so-called batch-type furnace, continuous furnace and the like have been provided.
The aforementioned surface hardening treatment methods of steel using the conventional hardening are being widely employed for production of various industrial products, however there were many problems in these methods because they utilize the martensitic structural components. In some cases, a satisfactory result can not be obtained by these methods in view of the surfacial hardness, that is, the mechanical properties such as the wear and abrasion resistance, pitching resistance and the like. In addition to that, a distortion of measurement in the steel part occurs by the hardening.